1. Field of the Invention
The present invention relates to an integrated circuit package.
2. Description of Related Art
Integrated circuits (ICs) are typically housed within a package that can be mounted to a printed circuit board. A conventional IC package includes an outer housing that encapsulates the integrated circuit and a lead frame that couples the circuit to the printed circuit board. The outer housing is typically constructed from a dielectric material such as a glass filled epoxy. Glass filled epoxies have a relatively low coefficient of thermal conductivity. Consequentially heat is dissipated poorly to the ambient and a substantial portion of the heat generated by the integrated circuit is transferred to the printed circuit board through the lead frame. The leads of the lead frame have a large thermal resistance which may cause excessive junction temperatures in the IC. High junction temperatures may damage or otherwise affect the performance and reliability of the circuit.
To improve thermal efficiency, some package designs employ a heat slug that is coupled to the integrated circuit and provides an alternate heat path. The heat slug is typically mounted to the integrated circuit and provides a direct thermal path between the IC and the housing. To assemble such a package, the heat slug is initially coupled to the integrated circuit and encapsulated by an uncured silica filled epoxy. The epoxy is then heated and cured to create a rugged outer housing.
Heat slugs are typically constructed from a thermally conductive material such as copper or aluminum. Copper and aluminum have coefficients of thermal expansion that are higher than the silicon integrated circuit and the glass filled epoxy. Thus when the IC, epoxy and heat slug are heated and then cooled, the higher expansion coefficient of the heat slug can warp or bend the cured outer housing. A warped housing makes it difficult to apply a finned heat sink to the package and therefore increases the cost of the product. A warped housing may also create interference when the package is surface mounted to a printed circuit board. It would therefore be desirable to have an integrated circuit package that is thermally efficient and is easy manufacture.